This application requests support for the 20th Gordon Research Conference on the Chemistry and Biology of Tetrapyrroles, to be held at Salve Regina University, Newport, RI, from July 25-30, 2004. This biennial interdisciplinary conference has stimulated collaborations between basic biologists, chemists and clinicians interested in tetrapyrroles for more than three decades. In association with proteins, tetrapyrroles serve diverse roles as biological redox catalysts, for harvesting of light energy, for oxygen activation/delivery and as signaling molecules. Free tetrapyrroles are also essential nutrients (e.g., vitamin B12), serve as regulators of gene expression (e.g., hemes) and have been utilized as therapeutic agents (e.g., photodynamic cancer therapy, target delivery of radionuclides). Owing to their photodynamic activity, toxicity and lipophilicity, the accumulation of tetrapyrroles (e.g., porphyrins, bilirubin) is associated with numerous pathologies of the skin, liver and brain. For these reasons, this conference represents an important venue for exchange between basic and applied researchers on tetrapyrroles and for refinement of new tools and therapies, which are under development by the biomedical industry. Funds requested in this application are targeted to support 15 investigators, including those who have not spoken previously at this conference, as well as graduate students and postdoctoral fellows. A new session is devoted to highlighting work from early career scientists. A second new session focuses on emerging concepts in tetrapyrrole biology, including recently discovered mammalian globins and directed evolution of cytochromes P450. There will be 21 invited speakers, a plenary lecturer and 9 discussion leaders, who have been selected for their scientific excellence, recent innovative work and breadth of the program. The remaining 100 conferees will be chosen to ensue a broad representation of women, ethnicity and young scientists from various disciplines in academia, medical research institutions and industry. Strengths of this Gordon conference are its disciplinary diversity, focus on new unpublished work, time for discussion, informal atmosphere and ban on dissemination of conference proceedings. [unreadable] [unreadable]